Dimensionally stable nonwoven web and method of manufacturing same

ABSTRACT

Nonwoven web materials are formed from multiconstituent filaments having the ability to self-bond without substantial polymer flow, disfiguration, or cross-sectional flattening when heat-treated, said multiconstituent filaments being spun from at least two different polymeric materials such that, in a given filament, a first fiber-forming polymeric material defines a matrix and a second polymeric material is dispersed therein in the form of discontinuous fibrils, said matrix comprising at least 50 percent by weight of the filament and having a lower melting point than said dispersed fibrils. The multiconstituent filaments may be combined with other fibrous or additive materials in a variety of ways depending on the use intended for the web.

United States Patent [72] Inventors Robert C. Wincklhoier Richmond;

Gene C. Weedon, Richmond; George H. Collingwood, Hopewell, all of Va.

Dec. 20, 1968 Oct. 26, 197 1 Allied Chemical Corporation New York, N.Y.

Continuation-impart of application Ser. No. 727,327, May 7, 1968, and a continuationin-part of 727,325, May 7, 1968.

[21 Appl. No. [22] Filed [45] Patented [73] Assignee [54] DIMENSIONALLY STABLE NONWOVEN WEB AND METHOD OF MANUFACTURING SAME [56] References Cited UNITED STATES PATENTS 2,500,282 3/1950 Francis 161/150 Primary Examiner-Robert F, Burnett Assistant ExaminerRoger L. May Allorneys-Roy H. Massengill and Luther A. Marsh ABSTRACT: Nonwoven web materials are formed from multiconstituent filaments having the ability to self-bond without substantial polymer flow, disfiguration, or cross-sectional flattening when heat-treated, said multiconstituent filaments being spun from at least two different polymeric materials such that, in a given filament, a first fiber-forming polymeric material defines a matrix and a second polymeric material is dispersed therein in the form of discontinuous fibrils, said matrix comprising at least 50 percent by weight of the filament and having a lower melting point than said dispersed fibrils. The multiconstituent filaments may be combined with other fibrous or additive materials in a variety of ways depending on the use intended for the web.

DIMENSIONALLY STABLE NONWOVEN WEB AND METHOD OF MANUFACTURING SAME This is a continuation-in-part of Ser. No. 727,327, filed May 7, 1968, for Dimensionally Stable Articles and Method of Manufacture and of Ser. No. 727,325, filed May 7, 1968, for Dimensionally Stable Articles and Method of Making Same."

BACKGROUND AND PRIOR ART Nonwoven web materials are the basis for making a great variety of products. For example, they are used for, or converted into products useful as filters, scouring materials, abrasive carriers, etc. Many other applications in apparel and other industries are well known.

illustrative of the art to which the subject matter hereof pertains are Stein, et al., U.S. Pat. No. 3,324,609 and Levy, U.S. Pat. No. 3,276,944. In Stein a web formed from fusible synthetic fibers is layered with a woven web and needle punched; the portion of the fusible fibers penetrating through the woven web as a result are then anchored by flame-induced fusion. Levy discloses a nonwoven web composed of one or more fibers of the same or different chemical compositions, which are highly oriented, and adapted to self'bond upon exposure to a certain nonsolvating fluid atmosphere, particularly steam.

Still other prior art disclosures include reference to use of low melting point and high melting polymers in the same nonwoven web, as for example, where certain bonding operations have employed cospun filaments, or composite filaments comprised of the two polymers in side-by-side relationship.

SUMMARY AND OBJECTS The present invention involves the formation of novel nonwoven web materials employed as end products or as intermediates to end products, but with advantages in composition which afford several benefits over the previous known materials. The latter are achieved by incorporating in the novel nonwoven web materials of this invention, multiconstituent filament composed of at least two fiber-forming polymeric materials combined in accordance with the principles set out in Twilley U.S. Pat. No. 3,369,057 (which patent is hereby incorporated by reference as if fully set out herein). Twilley originally disclosed multiconstituent filaments comprised of nylon 6 and a polyester prepared for employment in highstrength yarns, useful in yarn or cord form as reinforcing strands in elastomeric tires, conveyor belts, seat belts, hoses, and the like, resulting in improved strength, durability and shape retention of these articles. This same combination of materials and others produced in a similar manner are useful in the nonwoven webs hereof.

Several variations of the invention are contemplated. For example, the webs hereof are comprised of continuous filament and/or staple fibers which may be combined with other polymeric materials in the manner ofa bicomponent wherein filaments are extruded side by side in a single yarn or in the form of a mechanically blended yarn comprised of several filaments twisted, braided, etc., together by well-known methods. Thus, the web materials will contain multiconstituent filamentary material, but in various ways within the scope of the invention as will be described.

As used herein, multiconstituent means filaments made by inclusion of at least one polymeric material in a matrix of another by discontinuous fibrils, the two materials having substantially different melt temperatures such that fibrous constructions composed thereof can be bonded by application of heat below the melt temperature of one and equal to or above that of the other, the entire filament composition or any component thereof optionally including any secondary material compatible with the bonding process and end utility of the web as a whole, such as antioxidants and other stabilizing agents, reinforcing particles, fillers, adhesion promoting agents, fluorescent materials, dispersing agents, and others useful in polymerization, extruding, spinning, fabric forming and shaping, heat-setting and product-finishing techniques. if desired, inorganic materials such as metal whiskers, fiber glass fibrils, asbestos particles and the like may be incorporated for conductive and/or reinforcement purposes.

The preferred multiconstituents useful herein are comprised of a homogeneous mixture of two different polymeric materials, the lower melting material forming a matrix in which the higher melting material is dispersed throughout in the form of discontinuous microfibers. Although various polymeric materials together in accordance with this invention, they need not be entirely intermiscible due to their physical properties and/or the mixing technique employed to disperse the higher melting component in the matrix material for forming microfibers. Thus microsized globules or fibrils are usually initially produced in the matrix, which when spun or drawn, produce the desired microfibrillar dispersion in the lower melting matrix material. The filaments are generally of textile denier (approximately 1-17) for most applications, but higher or lower deniers of virtually any size are contemplated to be useful in the invention, for special applications. The fila ments may be crimped or straight and may be round, trilobal, elliptical, or any other cross-sectional shape.

The principal advantages offered 'by employing multiconstituent filament is the resultant self-bonding web produced, and the improved strength, tear, durability and the high degree of versatility the material offers as an intermediate for a great variety of articles. The principal object of the invention is, therefore, to provide novel nonwoven webs produced at least in part from multiconstituent yarn or filamentary material. Another object is to provide nonwoven webs produced from continuous filaments in the form of sheetlike structures, and to provide novel methods for producing the same from continuous filaments distributed in a homogeneous, random or oriented manner with a low degree of aggregating fibers, and more particularly, to provide such nonwoven webs embodying the improved strength and bonding properties of multiconstituent filaments in a substantially isotropric or oriented structure. A more specific object of the invention is to provide such nonwoven webs containing filamentary material comprised of two or more fiber forming polymeric materials combined together in a lower melting matrix, higher melting dispersion, relationship. Another object is to provide novel nonwoven webs which will self-bond by exposure to appropriate physical conditions without using a solvating agent or a foreign binder, and without destroying (or reducing to a major extent) the strength as determined by tongue tear or breaking strength methods. Other objects will be described and will become apparent to those skilled in this art from the appended claims and following description of the best mode of carrying out the invention and examples thereof.

The invention is applicable to any suitable web-forming procedure insofar as multiconstituent filaments comprise part of the web. Thus the webs hereof may be formed by wet-laying, by carding, by depositing staple fibers from a Rando Webber machine, or by any of the numerous continuous filament web-laydown processes. illustrative of the latter are disclosed in the following U.S. Pats. No. Vosburgh 3,368,934; Medeiros et al. 3,384,944; Kinney 3,341,394 and IBundy et al. 3,296,678. Still further novel continuous processes hereof will be described below.

The geometry of the filamentary web will vary considerably between filament compositions, method of web preparation, bonding system, if any, and the physical conditions to which the material is exposed during any of the above phases. In general the random positioning of highly oriented filaments produces the desired isotropic web which can exhibit strength advantages in any direction in the plane of a sheet of the web, the filaments being separate and independent for the most part,'except at crossover points. For any given application of a web, the strength in a particular direction for increased strength in the machine direction, for example, randomness for more isotropic strength, bunching, bonding, loft, fluid permeability, and all the various other properties known to the art, may be critical. However, for the purposes of this invention, the web can be formed from multiconstituent filament handled in a manner similar to other known filament web ingredients to produce the various properties for a given end product. Such manipulation is within the art and extensive discussion which could be given can be found, for example, in the several patents cited herein.

The nonwoven webs hereof are most useful in the form of bonded sheets and most of the following description will be in this vein. However, an unbonded web serves as a useful intermediate product which can be selectively shaped and bonded according to the particular needs of the end product desired. It has been disclosed in the above-identified copending applications that multiconstituent filaments have the ability to bond to each other, and to other filaments, in a manner which does not cause significant flow or cross-sectional disfiguration, thereby setting up conditions for bonding systems that promote fiber orientation and strength and yet which admit controllable physical properties such as porosity, permeability, appearance, texture, etc. It is preferred that bonded webs formed be deposited by a continuous yarn spraying technique such as a traversing spinnerette type process which promotes or facilitates rapid bonding of heat-softened filaments in a one or two step process.

The examples which are given below illustrate the production of unbonded webs as well as some of the many modifications of binder technology which may be employed in utiliza tion of the principles of this invention. Bonding procedures which may be employed are summarized here to illustrate the wide range of useful techniques. One desirable embodiment involves nonwoven structures which have been prepared in a form providing cospun binder fibers. Such binder fibers may consist of continuous filament of a similar chemical nature to the structural filament element but having a lower melting point. In one mode of operation, such binder filaments may be filaments of the same chemical composition but spun with a lower level of orientation or with no orientation. In a second mode of operation, the cospun binder filaments may be highly oriented but may be ofa copolymeric nature or of some other modification which provides a lower melting temperature.

Indeed it is not necessary that any different filaments be employed since the principle of self-bonding may be used, in which the bonds are provided by localized fusion, partial or complete of individual portions of the fibers. Such fusion may be brought about by spark discharge through the web or the application of heat to highly localized, mechanically isolated portions of the web. The instant nonwoven structures may also be rendered more stable to delamination by needling techniques (see, for example, Lauterbach & Norton, U.S. Pat. No. 2,908,064).

Bonding may be applied uniformly over the entire area of the fabric or in closely controlled patterned areas or in random patterned areas. Two or more difierent bonding techniques may be employed simultaneously or in sequence. In addition to bonding in itself, application of other materials to the nonwoven sheet structures of this invention may be employed for other purposes such as surfacing, modification of visual appearance or opacity or porosity or for providing other physical or chemical properties of a specific desired nature.

It is also possible to laminate the nonwoven structures of the present invention to films or fabrics which are in themselves thermoplastic or may contain thermoplastic elements which can be bonded to the present webs by the application of continuous or localized areas of heat. Within the scope of this aspect of the invention is included the lamination of the nonwoven sheet structures of this invention to metallic foils, and to impervious or pervious films. Such materials are useful for the preparation of protective coverings, vapor seals, conductive materials, dielectrics and other articles of commerce.

As to chemical makeup, the multiconstituent filaments are prepared from a combination of polymeric materials, one of which is capable of acting as a low melting matrix in which a higher melting dispersion is created by suitable mixing.

Polyester-polyamide combinations produce the most outstanding properties of any combination tested thus far. The compositions contain 50-90 parts by weight nylon 6 and 50l0 parts by weight of a polyester microfibrilar dispersion. Other particularly good materials in multiconstituents are polyolefins, polysulfones, polyphenyl oxides, polycarbonates, and other polyamides and polyesters. Examples of the most useful polyolefin materials are polyethylene, polypropylene, poly-l-butene, poly-Z-butene, polyisobutylene and polystyrene. In addition to the preferred nylon 6 (polycaproamide), other suitable polyamides are nylon 610 (hexamethylene-diamine-sebacic acid), nylon 6--6 (hexamethylene-diamine-adipic acid), methanoland ethanolsoluble polyamide copolymers and other substituted polyamides such as the alkoxy-substituted polyamides. The preferred polyester is polyethylene terephthalate; others are polyesters of high T useful in the practice of the present invention, including those polymers in which one of the recurring units in the polyester chain is the diacyl aromatic radical from terephthalic acid, isophthalic acid, S-t-butylisophthalate, a naphthalene dicarboxylic acid such as naphthalene 2,6 and 2,7 acids, a diphenyldicarboxylic acid, a diphenyl either dicarboxylic acid, a diphenyl alkylene dicarboxylic acid, a diphenyl sulfone dicarboxylic acid, an azo dibenzoid acid, a pyridine dicarboxylic acid, a quinoline dicarboxylic acid, and analogous aromatic species including the sulfonic acid analogues; diacyl radicals containing cyclopentane or cyclohexane rings between the acyl groups; and such radicals substituted in the ring, e. g., by alkyl or halo substituents.

The multiconstituent filaments may be used alone or in combination in the same yarn or as separate entities in the nonwoven web, including natural or synthetic origin, as for example, binder, filler, or to impart other characteristics to the web. Illustrative are vegetable fibers, mineral fibers such as asbestos and glass fibers. Of course any such material employed must be compatible with any other material used and with the process conditions under which the web is formed, bonded or finished.

EXAMPLE 1 The following specific example is the preferred embodiment of this invention. Multiconstituent filament is produced in accordance with the formulation of example I in U.S. Pat. No 3,369,057, i .e., granular polyethylene terephthalate polymer was used, melting about 255 C. (DTA) and about 265 C. (optical), having density (when amorphous) of about L33 grams per cc. at 23 C. and about 1.38 grams per cc. in the form of drawn filament, having reduced viscosity of about 0.85 and having T about 65 C. The polyester in the form of drawn filament drawn to give ultimate elongation of about 20 percent will have tensile modulus (modulus of elasticity) ranging from about 70 to grams per denier, depending on spinning conditions employed.

This polyester (30 parts) was mixed with 70 parts of granular polycaproamide having reduced viscosity about 1.04, T about 35 C. and density about 1.14 grams per cc. at 23 C. Amine groups in this polycaproamide had been blocked by reaction with sebacic acid, bringing the amine group analyses thereof to ll milliequivalents of Nl-l2 groups per kilogram of polymer. This polycaproamide contained as heat stabilizer, 50 p.p.mcopper as cupric acetate.

The mixture of polyamide and polyester granules was blended in a double cone blender for 1 hour. The granular blend was dried to a moisture content of no more than 0.01 percent; then melted at 285 C. in a 3Vz-inch-diameter screw extruder operated at a rotational speed of about 39 r.p.m. to produce a pressure of 3,000 p.s.i.g. at the outlet. A dry nitrogen atmosphere was used to protect the blend against absorbing moisture. Residence time in the extruder was 8 minutes.

The molten mixture thereby obtained had melt viscosity of about 2,000 poises at 285 C. The polyester was uniformly distributed throughout and had average particle diameter of EXAMPLE 7 about 2 microns, as observed by cooling and solidifying a sample of the melt, leaching out the polyamide component with formic acid, and examining the residual polyester material.

The multiconstituent blend thus produced hereafter referred to by code designation as AC-OOOl was formed into The same as example 6 except that yarn feed speeds were varied, ACO001, 740 and polyethylene terephthalate filaments 1,020 feet per minute, and the relative material amounts in the nonwoven product were 94 and 6 percent respectively.

heart-shaped yarn in cross section in a Well-known manner to give 16 denier per filament. It was then fed through apparatus such as describe in the above cited Kinney U.S. Patent, com- 7A 7B 7C 7D prising a pneumatic straight" jet. The latter is continuously supplied with 40 p.s.i.g. jet air pressure and caused to traverse press Fusion 2'5 220 225 220 across a receiver conveyor belt 37 times per minute, the latter Temp. c. conveyor belt speed being l6.l feet per minute. The web thus 2:? 'F Z3 38- T5 23 deposited was bonded by passing through a heating zone operating at 222 C. for a period of 10 seconds. The final wei mQL/ a. 3.15 3.50 3.01 3.43 bonded web was 4.5 oz./yd. with further data shown below in Break table 1. The fusion was carried out by a Pasadena Hot Press, was) CM Pasadena Press, Inc., Pasadena Cal. at 470 p.s.i. across a tex- M tured pattern. 1 Elong. m

i TABLE 1 Conveyor traverse Belt Trav. Jot air Example Speed strokes pressure Number Feed Yarn f.p.m. per min. i.s.i.g. Jet style 1 AC-OOOI Heart cross-section 16 d.p.f.r 1b 1 37 Straight. 2 AC-OOO] Round cross-secti0n 5 d.p.f 16. l 38 3 3 AC-OOOl Heart cross-section 15 d.p.f 16. 1 38 Oval orifi r outluL. 4 do 16.1 38 45 5 Nylon 6 cross-section 10 37 80 lo 1 in. strip breaking str. Tongue Fusion tear SLl'., Pounds Elongation lbs Shrinkage Fab. Example Temp, Time. nL boil. wt.. Number C. Type sec. M 1 CM M GM .\l CM pi-rcont oz./ vd. Y

222 Point 10 20. 0 l4. 5 16. 3 .23. 1 ll. 1 (i. l l) 4. 5 217 .do 10 32.7 .20. 3 10.2 15.8 4.0 3.0 0 4.2 225 0.00"... 8. 5.5 225 Improved point. 7. 4. 5 2:20 o 4.7

l Machine.

2 Cross 1111210111110.

The following examples are illustrative of nonwovens com- Break. 7.0 m4 prised of a multiconstituent and other yarn materials such as S 23.3 Dacron, polypropylene, nylon 6. etc. Tongue Tear l8 l3 (lbs) 2.5 2.3

EXAMPLE 6 45 CM Using the procedure given above for examples 1-5 in table 1, ACOOOl, denier 1125/70 having a heart-shape filament cross section and polyethylene terephthalate filaments of denier 60/34, round cross section, were fed in two passes onto a conveyor traveling at 8 feet per minute. Yarn speed was 990 yards per minute, and the relative amounts of each yarn was EXAMPLE 8 95 to 5 percent respectively.

The same as example 6 with AC-OOOI denier l 125/70 and acetate yarn denier l50/38 round, yarn feed speeds andreiative amounts in the web being l,OO0 and 1,080 f.p.m. and 87 and 13 percent respectively.

Press Fusion 2l0 210 210 215 Temp. C. Ram Force 20,000 30,000 30.000 30.000 8A 8B 8C 8D Fusion Time l0 15 30 15 (Sec) V weigh oz'lydl, 16' 367 3J0 3'24 Press Fusion 225 225 225 225 Breaking Strength 3.75 5.79 Temp' o abs.) 0A0 40 Ram Force 20,000 20.000 20.000 20,000 Fusion 20 2o 20 TirlG (Sec.) .4 22: 3 Tm 4 7 3 4 1 Weight ozJyd. 2.47 1.93 2.52 2.23

' CM" Break. Str. l4.6 l8.2

CM M Rum force indicates the pressure on an 8 Tongue Tear T (lbs-l 0.42 0.52 -inch square. CM

"Cross machine. M

' "Machine.

EXAMPLE 9 The same as example 6 but using two ends of AC-0001, denier l 125/70 heart cross section and one end of polypropylene denier 3750/210 round cross section. The feed speeds onto a conveyor running at 14 f.p.m. were 1,350 and 620 f.p.m. respectively, and the resultant web contained 40 and 60 percent of the two materials respectively.

9A 9B 9C 9D Press Fusion 225 225 225 225 Temp. C. Ram Force 20,000 20,000 10,000 5,000 Fusion Time 15 5 5 (sec.)

(w/screens) Weight oz./yd. 4.00 4.52 5.10 5.48 Break. Strength 20.6 26.8 (lbs) 15.4 14.2

l Elong. at 22.9 22.9 Break 1 1.8 12.0

Tongue Tear 14.8 3.4

(lbs.) 9.7 3.6

In 9 A a screening device consisting of 10 -mesh and 20 EXAMPLE 10 Same as example 6 utilizing one end of the following:

Denier Cross Section Feed Amount (f.p.m.) (1) AC-OOOI 1.125/70 Heart 1,300 Nylon 6 1,125/70 Y 1.630 14 Undrawn 6.000/192 Round 1,630 71 Polyester The receiving conveyor was operated at 13 f.p.m.

10A 10B 10C Press Fusion 200 200 200 Temp. C. Ram Force 10.000 20,000 5.000

Fusion Time 10 I0 5 (sec.) Weight oL/yd. 11.86 7.86 10.88

Break. Str. 23.1

k Elong. at Break Tongue Tear 6.3 9.1 (1135.)

In another embodiment of the invention, economies are achieved by laying the nonwoven web material down continuously, while hot, in a heated zone, the latter being maintained at a melting components. For example, the AC-0001 material of Example 1 can be fed through apparatus of the type described in Bundy U.S. Pat. No. 3,296,678, wherein the filamentary material is laid down in random nonparallel arrangement by means of a moving jet. Contained in the jet of Bundy is a relaxing chamber in which the filament material is heated prior to exit therefrom. This preheating is desirable up to the point of deleterious effect on the web laid down. The heat transfer fluid should therefore be approximately l-205 C. for best results. A conveyor belt passing through an open zone of radiant gas or electric heaters receives the web, the unpressurized zone temperature being approximately 240245. Residence time in the zone depends on the extent of fusion desired, 5-30 seconds being sufficient to effect fusion of available contact points from 10 percent to approximately percent.

Variations of the above can be employed; for example, fusion can be effected by spraying molten filamentary material on a conveyor, which can but need not be in a heated zone, or the conveyor itself can be heated sufficiently to effect fusion, particularly where fusion on only one side of a web may be desired.

Where bonding by heating to effect fusion is carried out, it should be apparent that for any given web and/or multiconstituent formulation contained therein, a wide variety of physical conditions exist which will provide desirable properties, depending on the intended utility of the web. Temperature and heating time will vary depending on the polymeric materials, article size, shape, pressure applied, etc. it is even possible for a web comprised predominantly of multiconstituents to be heated to such an extent it will take on a set shape. In general, when bonding multiconstituents it is desirable to apply heat at a temperature above the lower melting polymeric component, the matrix, but below that of the higher melting component. By this procedure an effective bonding is achieved yet all of the strength and other properties of the dispersed component remains undisturbed.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are, therefore, to be embraced therein.

We claim:

1. A dimensionally stable nonwoven web of heattreated fusion bonded, nonwoven, nonparallel and random filamentary materials; said filamentary materials being comprised of at least 15 percent by weight of multiconstituent filaments spun from at least two different polymeric materials such that, in a given filament, a first fiber-forming polymeric material defines a matrix and a second polymeric material is dispersed therein in the form of discontinuous fibrils, said matrix comprising at least 50 percent by weight of the filament and having a lower melting point than said dispersed fibrils; and said filamentary materials having been heat-treated at a temperature in the range above the melting point of the matrix but below the melting point of the dispersed fibrils such that the multiconstituent filaments thereof are set and fusion bonded at least at their cross points without substantial polymer flow, disfiguration, and cross-sectional flattening; whereby a nonwoven textile appearance is retained and said fused nonwoven filamentary material is characterized by enhanced strength, stiffness, tear and durability.

2. A nonwoven web as defined in claim 1 wherein said multiconstituent fibrous material is comprised of a polyamide and a polyester in amounts ranging from 50-90 and 50-10 parts by weight, respectively.

3. A nonwoven web as defined in claim 2 wherein said polyamide is nylon 6 and said polyester is polethylene terephthalate.

4. A nonwoven web as defined in claim 1 wherein said filamentary materials are continuous.

5. A nonwoven web as defined in claim 1 wherein said filamentary material is comprised substantially completely of a multiconstituent.

6. A nonwoven web as defined in claim wherein said multiconstituent is comprised of a polyamide and a polyester in amounts ranging between 50-90 and 50-10 parts by weight, respectively.

7. A nonwoven web as defined in claim 1 wherein filamentary materials are separate continuous ends randomly laid down in a sheet, and wherein said multiconstituent fibrous materials are bonded together 8. A nonwoven web as defined in claim 1 wherein the filamentary materials are staple fibers.

9. A nonwoven web as defined in claim 1 wherein a portion of the filamentary materials are staple fibers.

10. A nonwoven web as defined in claim 1 wherein said filamentary materials have been heattreated under such pressure that fusion is effected at diminished temperatures.

11. A nonwoven web as defined in claim 1 wherein said filamentary materials are substantially isotropic.

12. A nonwoven web as defined in claim 1 further comprised of a member selected from the group consisting of metal whiskers, fiber glass fibrils and asbestos particles.

13. The method of manufacturing the dimensionally stable nonwoven web as defined in claim 1, comprising:

i. laying down a continuous sheet of nonwoven, nonparallel and random filamentary material comprised of at least percent by weight of multiconstituent filaments spun from at least two different polymeric materials such that, in a given filament, a first fiber-forming polymeric materia] defines a matrix and a second polymeric material is dispersed therein in the form of discontinuous fibrils, said matrix comprising at least about 50 percent by weight of the filament and having a lower melting point than said dispersed fibrils; and

ii. heat-treating and fusion bonding said filamentary material at a temperature in the range above the melting point of the matrix but below the melting point of the dispersed fibrils such that the multiconstituent filaments thereof are set and fusion bonded at least at their cross points without substantial polymer flow, disfiguration, and cross-sectional flattening, whereby a nonwoven textile appearance is retained and the resultant fused nonwoven filamentary material is characterized by enhanced strength, stiffness, tear and durability.

14. A method of making a bonded nonwoven web as defined in claim 13 wherein said filaments are laid down under temperature conditions sufficient to promote bonding by fusion together simultaneously with said laydown procedure.

15. A method of making a bonded nonwoven web as defined in claim 14 wherein said sheet of freshly laid filaments is pressed while still warm to mechanically effect bonding by fusion.

16. A method of making a bonded nonwoven web as defined in claim 13 wherein the heat treatment is under such pressure that fusion is effected at diminished temperatures. 

2. A nonwoven web as defined in claim 1 wherein said multiconstituent fibrous material is comprised of a polyamide and a polyester in amounts ranging from 50-90 and 50-10 parts by weight, respectively.
 3. A nonwoven web as defined in claim 2 wherein said polyamide is nylon 6 and said polyester is polethylene terephthalate.
 4. A nonwoven web as defined in claim 1 wherein said filamentary materials are continuous.
 5. A nonwoven web as defined in claim 1 whErein said filamentary material is comprised substantially completely of a multiconstituent.
 6. A nonwoven web as defined in claim 5 wherein said multiconstituent is comprised of a polyamide and a polyester in amounts ranging between 50-90 and 50-10 parts by weight, respectively.
 7. A nonwoven web as defined in claim 1 wherein said filamentary materials are separate continuous ends randomly laid down in a sheet, and wherein said multiconstituent fibrous materials are bonded together.
 8. A nonwoven web as defined in claim 1 wherein the filamentary materials are staple fibers.
 9. A nonwoven web as defined in claim 1 wherein a portion of the filamentary materials are staple fibers.
 10. A nonwoven web as defined in claim 1 wherein said filamentary materials have been heattreated under such pressure that fusion is effected at diminished temperatures.
 11. A nonwoven web as defined in claim 1 wherein said filamentary materials are substantially isotropic.
 12. A nonwoven web as defined in claim 1 further comprised of a member selected from the group consisting of metal whiskers, fiber glass fibrils and asbestos particles.
 13. The method of manufacturing the dimensionally stable nonwoven web as defined in claim 1, comprising: i. laying down a continuous sheet of nonwoven, nonparallel and random filamentary material comprised of at least 15 percent by weight of multiconstituent filaments spun from at least two different polymeric materials such that, in a given filament, a first fiber-forming polymeric material defines a matrix and a second polymeric material is dispersed therein in the form of discontinuous fibrils, said matrix comprising at least about 50 percent by weight of the filament and having a lower melting point than said dispersed fibrils; and ii. heat-treating and fusion bonding said filamentary material at a temperature in the range above the melting point of the matrix but below the melting point of the dispersed fibrils such that the multiconstituent filaments thereof are set and fusion bonded at least at their cross points without substantial polymer flow, disfiguration, and cross-sectional flattening, whereby a nonwoven textile appearance is retained and the resultant fused nonwoven filamentary material is characterized by enhanced strength, stiffness, tear and durability.
 14. A method of making a bonded nonwoven web as defined in claim 13 wherein said filaments are laid down under temperature conditions sufficient to promote bonding by fusion together simultaneously with said laydown procedure.
 15. A method of making a bonded nonwoven web as defined in claim 14 wherein said sheet of freshly laid filaments is pressed while still warm to mechanically effect bonding by fusion.
 16. A method of making a bonded nonwoven web as defined in claim 13 wherein the heat treatment is under such pressure that fusion is effected at diminished temperatures. 